In recent years, a variety of optical transmission systems has been studied in which client data output from client devices is transmitted in frames. Among these transmission systems, particularly the OTN (Optical Transport Network) system has been drawing attention. The OTN transparently transmits client data in the SONET (Synchronous Optical Network) format or the SDH (Synchronous Digital Hierarchy) format.
The OTN system stores client data in a frame called OTU (Optical channel Transport Unit) frame standardized by ITU-T (International Telecommunication Union-Telecommunication standardization sector). Specifically, the OTN system stores client data in a payload area included in the OTU frame.
An FS (Fixed Stuff) byte area for storing fixed data is inserted in the OTU frame in some cases to match the bit rate of the client data and the bit rate of the payload area. Insertion of the FS byte area into the OTU frame causes an actual data area of the payload area available for storing the client data to be reduced. Accordingly, the OTN system stores the client data in the data area reduced by the FS byte area.
The related art includes Japanese Laid-open Patent Publication Nos. 2008-113394 and 2008-113395.